1. Field of the Invention
The present invention generally relates to computer data storage media and more particularly to life span enhancement of the read/write media.
2. Description of the Related Art
Magnetic media, optical media and electronic media form the bulk of the computer data storage media. Of these media, the magnetic media technology is relatively more mature as compared to the other media technologies. Hard drives, floppy disks and tape drives are well known forms of magnetic data storage media. The hard drives have become very reliable, and the technology is well developed. Since the read/write head does not touch the media, the number of rewrite cycles on a hard drive does not significantly impact its life span. In case of floppy drives and tape drives, however, the read/write head comes in contact with the media during the write cycles and thus impacts the life span of the media. The reason CD-R/W media wears out is that two different lasers are used in the read-write operations. The one to erase the media literally melts the substrate and causes the previous pits that were burned in it to disappear. The second laser that writes on the media is more gentle and just burns the little pits. Common file system based techniques to write data on the storage medium use file allocation table (FAT) schemes in which the first available area of the media is allocated for writing or rewriting the file. Further, a file directory on the media is typically located in the initial or beginning area of the media, and this directory is constantly updated with each write cycle. Certain areas of the media, like the file directory, undergo excessive write cycles and tend to degrade much faster than other areas.
Optical media provide large data storage capacity in relatively smaller volume and have become quite economical and thus attractive as a medium of choice. However, the life span of the read/write optical media, commonly referred to as CD-RW, is limited by the write cycles that the media experience. Typically, the optical read/write media has a film material with a solid backing. The write operation is performed by a laser that forms a bit pattern of the information on the film material. During the rewrite cycle, the laser melds the old bit pattern and forms a new bit pattern on the same film. There are two dominant factors that affect the life span of a CD-RW. First, different manufacturers use different film material which range in the number of rewrite cycles they can withstand. Second, different drive manufacturers use different amounts of laser power to write the data on the film. A higher powered laser is generally expected to make a deeper bit pattern and, therefore, provides a more reliable data bit pattern on the film. The capacity of the film to withstand rewrite cycles is reduced because of the lower meld-healing capacity of the film. Thus, a CD-ROM has a limited life since the film may experience the highest number of rewrites that the film can withstand. This unnecessarily shortens the life of the CD-ROM since even one file repeatedly written on a particular region on the CD-ROM degrades that particular CD-ROM area.
In a similar fashion, floppy drives of different capacities suffer excessive degradation of only some sectors where a file, for example the directory file or information, undergoes more revisions than other files. Also, electrically erasable storage media, such as a Sony Memory Stick for example, have limited write cycle life span, and therefore, excessive writing on only a limited region of the media may make the entire media unusable depending on the writing scheme. Thus, rewrite cycles exact a penalty for any read/write storage media involving contact with a write head. In an effort to limit this penalty, one approach has been to reduce the number of rewrite cycles to a disk through write buffering techniques.